Using a lensometer (HD).

In this video, I wanted to show you how
to use the lensometer.

The lensometer is a device used
for checking prescription glasses

and can be a little confusing.

The first step is to put the glasses
and the frames here,

and you can see this platform moves
up and down.

And you want to put
the optical center of this lens

such that it aligns here,

and this little brace
holds the glasses in place.

You want to make sure both glasses

are touching the bottom
of this platform.

Turn it on, and then look
through this eye piece,

and this is what you should see.

Now, the hard part
with using this machine

is you have to use two dials
at the same time.

There's an axis dial up here

and there is a focus dial
down here.

And you spin both of these,

and the goal
is to get the three small lines--

the three little lines next
to each other,

lined up and in focus.

So if we zoom in,
we can see that there's three lines.

You want to get them lined up
and in focus.

And then you can mark
down what this is.

If you look on our dial here
and our focus,

we can see this is a 3.25,
so that's the sphere.

The sphere is 3.25.

Now you move the focus
in whatever direction it takes

in order to get the three fat lines
in focus.

And the difference
between those is your cylinder power.

So we went up +2.75 to get to 6.0.

So that's our cylinder, +2.75.

Our axis looks like it's
about 12 degrees.

So here is our prescription.

Now, to get the bifocal power,

I need to move the glasses up
to the bifocal segment

and see how much
you need to change it

to get the three fat lines
in focus again.

So we went from +6.0 to +8.5,

so our add is +2.50.